I. Field of the Invention
The invention relates generally to a cordless telephone system, and more particularly, to a non-DSP (Digital Signal Processing) or non-digital telephone system having a handset handsfree speakerphone feature.
II. Background of the Invention
As shown in FIG. 1, a typical cordless telephone system 10 includes a base unit 11 and at least one cordless handset 12. Base unit 11 is coupled to PSTN 13 via a PSTN interface and communicates with cordless handset 12 via an air interface 14. In operation, when a far end user 15 is speaking, the audio will travel through a telephone line to a line interface circuitry (Hybrid) 111 of base unit 11. The audio is then gone through some gain adjustment and filtering before it is sent to an RF module 112 of the base unit 11. RF module 112 modulates the audio signal to an RF signal for being transmitted by a transceiver 115 via air interface 14 such as an FM radio to cordless handset 12. Cordless handset 12 includes a transceiver 125 that receives the RF signal from base unit 11, an RF module 122 that demodulates the RF signal to the original audio. A receiver 121 of cordless handset 12 receives the original audio and converts the demodulated signal to sound so that a user (not shown) can hear the speech from the far end user. Similarly, when the user speaks, a microphone 123 of cordless handset 12 converts the speech to an electrical signal that is then modulated by RF module 122 and is sent out to base unit 11, where it is demodulated and sent to Hybrid 111 and transmitted to far-end user 15 via PSTN 13.
For digital cordless telephone system, either base unit 11 or handset 12 can also include a DSP (Digital Signal Processor) or a digital means such as a powerful microprocessor 113 (only shown in base unit 11 of FIG. 1) to process an embedded speakerphone algorithm that supports a handsfree function. By means of the handsfree speakerphone algorithm, a user can make/receive a telephone call without picking up the handset.
Traditionally, it is difficult to implement the handsfree speakerphone function on a cordless handset of a cordless telephone system that is not equipped with a DSP or microprocessor, for example, an analog telephone system, that can process the embedded speakerphone algorithm. One possible solution to implement such feature is to design with “off the shelf” analog speakerphone IC in the cordless handset. However, the physical size of the IC and its supporting components makes it almost impossible to fit into a normal size handset.
Accordingly, there is a need to design a cordless telephone system that does no equipped with the DSP or digital means to support the handsfree speakerphone function of a normal cordless handset without changing the design of the cordless handset.